Project Summary/Abstract B follicular helper T (Tfh) cells are essential participants of both normal immune responses and autoimmune disease. Tfh cells function to coordinate humoral responses through contact dependent and independent help signals to B cells in the germinal centers (GCs) of secondary lymphoid organs. Within GCs, Tfh cells support B cell proliferation and survival, immunoglobulin affinity maturation, and memory B cell and plasma cell formation. In the autoimmune setting, Tfh promote aberrant GC B cell and memory B cell responses that contribute to autoantibody induced pathology. Disruption of this axis of help provides clinical benefit. The mechanisms that dictate Tfh cell function, differentiation, and survival are incompletely described, however. Upon differentiation, effector CD4 T cells change in bioenergetic demand and adopt metabolic profiles compatible with their proliferative and functional needs. We recently demonstrated that Tfh cells are not only functionally and spatially different from their Th1 counterparts, but also represent a metabolically distinct subset in response to acute viral infection, an environment flexible for experimentation and mimicry of the elevated type I interferon signaling in autoimmune diseases like systemic lupus erythematosus. This project aims to provide further insight into the metabolic programs defined by and required for Tfh cell differentiation. The two following specific aims will address the hypothesis that Tfh cells require distinct metabolic programs for their differentiation and function in vivo. In Aim 1, we will conduct a targeted CRISPR/Cas9 knockout library screen of all genes in the mouse metabolome, a set defined by genes encoding all enzymes, membrane transporters and channels, and cofactors that govern cellular metabolism. This will determine metabolic regulators of Tfh and Th1 cell differentiation and function. We will use this initial screen to validate pathways of interest, to build a metabolome map of T cell regulatory pathways, and to discover novel targets of inhibition to effect Tfh cell differentiation. Aim 2 will interrogate the fatty acid synthesis pathway in Tfh development and function, as previous work has implicated regulators of this pathway as important for Tfh cell identity. Further, a preliminary screen implicated a requirement for multiple genes in this pathway for Tfh cell differentiation and/or survival. In addition, this fellowship proposal presents the applicant's research career plan, describing in detail how the resources available to him within the Yale Immunobiology Graduate Program, his choice of Drs. Joe Craft and Richard Flavell as co-mentors, and his plans for professional and ethical development will serve him in becoming an independent biomedical academic research scientist.